Pressuremeter Tests Research Articles

Analytical analysis of cylindrical cavity expansion considering particle breakage effect of sand and its application for cone penetration tests

AbstractThe particle breakage effect in sand exerts a significant influence on the design of underground space structure. However, the existing theories seldom consider the breakage effect and often lack accurate descriptions of void ratio changes, leading to substantial errors in the numerical calculations compared to the actual scenario. This study employs the simple critical state sand model (SIMSAND) to account for the particle breakage effect and transforms the drained cylindrical cavity expansion problem into a set of first‐order ordinary differential equations described by the Lagrangian method. The analytical solution of the cylindrical cavity expansion problem is calculated using Matlab programming codes. Firstly, Fontainebleau sand is investigated to analyse the influence of initial stress, void ratio and specific volume around the cavity. The combined effects of initial stress and particle breakage on the soil around the cavities result in dilatancy characteristics and a reduction in void ratio. The stress path analysis reveals that the soil around the cavities only reaches a critical state under high initial stresses. Secondly, a plane strain numerical model is established for twice expansion to verify the calculation outcomes from the cylindrical cavity expansion theory. Finally, an axisymmetric cone penetration test (CPT) model is developed to analyse the theoretical and numerical solutions for expansion stress and sleeve friction. The research results indicate that the CPT in sand need to consider the particle breakage effect, especially under high stress conditions. Without considering particle breakage, the sleeve friction is overestimated. These research findings can offer guidance for geotechnical engineering applications, such as CPT, pressuremeter tests and predictions of bearing capacity for pile foundations in sand.

A Practical Design Method for Energy Piles Based on Pressuremeter Test Results

A Practical Design Method for Energy Piles Based on Pressuremeter Test Results

Cavity expansions in two silty tailings with high degrees of saturation and a comparison to CPT results

Tailings, being mixtures of water and soil-sized particles, and sometimes air, are waste products generated by mining. They are stored on sites, often contained by embankments, forming what are known as tailings storage facilities (TSFs). Assessments of the state and strength of tailings inside a TSF may involve in situ tests, especially the cone penetration test (CPT) and occasionally the pressuremeter test (PMT). Cavity expansion theory may assist the interpretation of these tests. The coexistence of air and water in the pore space means the tailings is unsaturated and gives rise to a suction. The suction, and the extent to which air and/or water can drain through the pores, affects the cavity expansion results as well as CPT and PMT results. The cavity expansion problem is solved here considering four possible drainage conditions, constant suction, constant water mass, constant contribution of suction to the effective stress, and a constant air and water mass (closed system). It is reasoned that solutions for a closed system are relevant to the interpretations of CPTs and PMTs when < 15 % of the tailings volume is occupied by air, and that the constant effective stress condition (which is a close approximation to a constant water mass condition) is relevant when larger air volumes are present. By considering CPT data it is observed that linear proportionalities exist between effective cone penetration resistances and cavity wall pressures. The cavity expansion results are then converted to equivalent CPT results and used to construct charts which relate the normalised cone penetration resistance to the initial state parameter. The charts have use for unsaturated conditions and a variety of air volume fractions, as well as saturated conditions when the cone penetration rate is slow enough so drained conditions prevail or fast enough so that undrained conditions prevail.

In-situ Creep Behavior of Expansive Soils Based on Pressuremeter Test

In-situ Creep Behavior of Expansive Soils Based on Pressuremeter Test

A sectorisation-based method for geostatistical modeling of pressuremeter test data: Application to the Grand Paris Express project (France)

In the context of underground construction projects such as large-scale linear projects, knowledge of subsoil geotechnical properties is of major importance. An effective way to analyze and represent the variability of these properties is to use geostatistical methods. Despite the good performance of such methods, their use is not yet widespread in the field of underground projects. This paper aims to show the usefulness of geostatistics in the field of tunneling by proposing an original 3D sectoral modeling approach that allows dividing the geological formations in homogeneous geotechnical areas to better take into account the vertical and lateral variations of geotechnical properties. The approach is tested by developing a 3D geostatistical model of the pressuremeter tests on a section of a massive tunneling project in Paris (France): the Grand Paris Express. A strong focus is also made on the model input data: a methodology is proposed to overcome the limitations of the pressuremeter test in order to better study the spatial variability of the net limit pressure. A twofold analysis is conducted by comparing the modeling results obtained with and without pressuremeter data processing and those obtained with and without sectoral modeling. The results of the comparison show that: a) data processing is useful to better discern areas of extremes values of net limit pressure; b) dividing the geological units into homogeneous geotechnical sectors provides an advantage for geological units with geotechnical heterogeneities, as it leads to improved reliability of results.

Loading-unloading of spherical and cylindrical cavities in cohesive-frictional materials with arbitrary radially symmetric boundary conditions

Many scenarios in geotechnical engineering involve cavity unloading from a loaded state under different boundary conditions, especially for thick-walled cylinder tests in laboratory conditions. A novel analytical cavity expansion-contraction solution is proposed for modeling thick-walled cylinder tests during a complete loading-unloading process under arbitrary symmetric boundary conditions. The proposed solution has potential implication in investigating ambiguous boundary effects for problems involving cavity expansion-contraction. The mechanical model considers two concentric layers of materials around the cavity, where the inner layer is considered as cohesive-frictional and the circumambient infinite layer is assumed as elastic to simulate the arbitrary radially symmetric boundary condition, including two extreme scenarios with constant-pressure and zero-displacement boundaries. The derived solution provides the evolutions of cavity pressure and distributions of stresses and displacements in both layers during the loading-unloading process, which is then rigorously validated against finite element results. The effects of boundary conditions and size of the cohesive-frictional layer have been comprehensively investigated by analyzing the cavity pressure and the developments of plastic zones during expansion and contraction. The developed solution has been proved to be applicable in geotechnical engineering, with comparisons between analytical results and experimental data for pressuremeter tests in calibration chambers and pile installation tests in a rigid container. The proposed solution might also be helpful in the analysis of autofrettaged pressure vessels.

Cavity expansions in partially drained soils and a comparison to CPT results

Cylindrical and spherical cavity expansions in soils are of interest, especially when interpreting cone penetration tests (CPTs) and pressuremeter tests (PMTs). Here the cavity expansion problem is solved semi-analytically, considering partial drainage of the soil, when the cavity wall velocity is constant. The solutions may assist with the interpretation of CPTs and PMTs when partially drained conditions prevail in the surrounding soils. The solution procedure involves writing the governing partial differential equations in dimensionless form. The modified Cam-clay constitutive model is adopted for the soil to demonstrate the solution procedure, due to its wide familiarity, although other models could be used by making simple modifications. The variables in the partial differential equations are functions of a dimensionless time, T, and a dimensionless radial coordinate, H. T depends on cavity radius, the time after expansion began and a coefficient of consolidation. The equations are solved for when T is fixed, simultaneously as an initial value problem, as the partial differential equations become ordinary differential equations. Important features captured by the analyses include pore water pressure variations with soil volume changes, as well as the differential of the pore water pressure satisfying the no-flow cavity wall boundary condition. Results for a cavity expansion reveal that initially, when T and the cavity are small, drained conditions prevail. As T and the cavity become larger the soil becomes partially drained and eventually undrained. T is analogous to the dimensionless cone penetration velocity used in CPT studies. Normalised cavity wall pressures vary with T similar to that of normalised cone penetration resistances, demonstrated using experimental data. Plots of the normalised cavity wall pressures against the state parameter show that the two key fitting constants are heavily influenced by partial drainage. A similar dependence must exist when plotting a normalised cone penetration resistance against the state parameter when partially drained conditions prevail. The practical ramifications of not dealing with this partial drainage may be huge, especially when assessing liquefaction susceptibility through estimations of the state parameter using correlations developed for when drained conditions prevail. Significant underestimations of state parameter, liquefaction susceptibility and post-liquefaction strengths may result.

Assessing combined analysis of electrical resistivity tomography and multichannel analysis of surface waves for ground improvement assessment near by-pass road, Silchar, Assam

Soft clayey soils are generally improved by the consolidation process. The different improvement techniques which are in vogue include the use of stone columns, sand drains with and without preload and prefabricated vertical drains. Upon improvement, the soft soil attains a higher strength and better resistance to excessive settlement. The extent of this improvement of the soft soil is measured through different in-situ tests including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Pressuremeter Test. Most of these tests are invasive and require boreholes for the collection of soil samples. Geophysical tests can scan the entire area within a short time and can accurately interpret the extent of the improvement depending on the expertise of the investigators. Sometimes a combination of two or more geophysical tests is suitable for an accurate prediction of any change in soil properties. The present study is an attempt to measure the effect of ground treatment by implementing two types of geophysical tests, namely, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Wave (MASW) near a by-pass road in Silchar, Assam. The tests were conducted on a newly constructed road embankment that had undergone excessive settlement and was subsequently treated with stone columns with a preload. Both the geophysical tests showed improvement in soil properties as well as in the bearing capacity of the original soft soil. A bore log survey was also carried out before the improvement work to validate the results of the geophysical tests. Existing correlations among geophysical properties and soil properties were used to obtain the effect of improvement. It has been observed that geophysical tests can easily be carried out to accurately calculate the effect of improvement of soil properties. A combination of two or more geophysical methods yields a better understanding of the post-treatment results.

Evaluating the efficiency of stone columns in mitigating liquefaction risks and enhancing soil bearing capacity: A case study

Several processes allow the improvement of soils such as vibrocompaction, stony columns, static horizontal compaction etc. These processes reduce the risk of liquefaction potential and making it possible to build on this type of soil when the space restriction require it. Stone columns are a recognized method of soil improvement, which consists of creating large diameter columns using special vibrators with granular filling materials introduced into the ground. The objective of this work is to evaluate the effectiveness of stone columns, made in a seismic zone containing liquefiable materials, with regards to the reduction of the risk of liquefaction and the improvement of the bearing capacity of the soil. The approach followed is the exploitation of geotechnical investigation tests (CPT Cone Penetration Test), (SPT: Cone Penetration Test, (pressuremeter tests), carried out before and after soil treatment. This study showed that the network of gravelled columns produces an enhanced soil improvement effect by improving the modulus of elasticity of the soil and reducing settlement and the risk of liquefaction after treatment. The process allows for the improvement of the geotechnical characteristics of its soils, making it possible to build infrastructure and development projects in the area.

French practice for design of embedded walls: history and background, overview of limitations of different models and design approaches

French practice for the design of embedded walls intensively relies on active and passive limit equilibrium analyses, in the tradition of the work by Coulomb, Caquot, Kérisel and Absi, as well as on the more recent method involving spring coefficients, the use of which has become almost systematic, in the continuity of the approaches initiated by Terzaghi and Ménard. This latter method has ever since been improved and refined by intensive geotechnical monitoring, and is of course substantiated, as needed, by the finite element method. The parameters needed to check the serviceability limit states are most often derived from pressuremeter tests, interpreted in accordance with the principles initially established by Ménard, but here again refined by the feedback of monitoring. The ultimate limit states are traditionally checked using global safety factors (approach 2 or now RFA as defined in EC7), the partial factors on the soil resistance parameters (approach 3 or now MFA) being used only for certain situations or types of structures. This tradition, built up on pragmatism, that excludes the unconditional use of a systematic approach and a single method, is based on the belief, every day strengthened by observation and measurement of the behavior of structures, that there is no unique model that would apply to all situations, and that, on the contrary, identification of the limits of existing models is essential. In this lecture, we propose to present the different aspects of this national practice by explaining not only the backgrounds, but also the limits, as well as the way they are taken into account, or at least they should be when this is not the case.

Developments in the seismic CPT and links to the Ménard Pressuremeter Test

The seismic cone penetration test (SCPT) was developed in the early 1980s and significant developments have been made in its use and application. This paper provides a review of these developments with particular emphasis on its application to identify soil microstructure. The Ménard pre-bored pressuremeter test (PMT) is one of the most popular in situ tests in France and links between SCPT results and the PMT are suggested.

Solution of the inverse analysis problem in geotechnics using stochastic methods—application to a pressuremeter test

Solution of the inverse analysis problem in geotechnics using stochastic methods—application to a pressuremeter test

A correlation based on pressuremeter, SPT and CPT tests for characterizing of coastal alluvium: A study for phase 14 South Pars, Iran

Pressuremeter Test (PMT), Cone Penetration Test (CPT), and Standard Penetration Test (SPT) are the key in-situ experiments to directly estimate the in-situ modulus of deformation and strength parameters of soils, which are highly used in coastal alluvium. In addition, CPT and SPT are unique tests for estimating engineering properties that are ideal for onshore regions. These tests are adaptable for coastal alluvium with different saturation levels, which facilitates the determination of the field deformation modulus. Regression analysis, on the other hand, is primarily employed to estimate the empirical relationship between measured parameters and to predict geo-engineering properties. This technique is typically used to estimate the in-situ modulus of deformation and strength parameters from CPT, SPT, and PMT results. The proposed formulas in this paper used regression to correlate and characterize coastal alluvium located in phase 14 South Pars (Assalouyeh) and were compared with previously published equations. As a result of the evaluations, the correlations provided for phase 14 South Pars can be expressed as Em = 0.442 qc + 2.221 (R2 = 0.999) and PL = 0.06 Em0.778 (R2 = 0.515).•This empirical method can be useful for ground assessment and estimating the in-situ modulus of deformation.•This relationship can use as a modification for the original formula used based on CPT-PMT-SPT for alluvium.•This empirical correlation provides fast and reliable data for Southwest Iran nearby the Persian Gulf.

"Ladetes"-A novel device to test deformation behaviors of hydrate-bearing sediments.

Natural gas hydrate (NGH) exploitation is severely restricted by geotechnical problems. Deformation behaviors of the hydrate-bearing strata (HBS) control the occurrence and evolution of geotechnical problems during extracting natural gas from HBS. In this paper, a novel approach named Ladetes is introduced to evaluate the lateral deformation behaviors of the near-wellbore and fracture-filling regions of the HBS. The pressuremeter test and the flat dilatometer test are designed to simulate the inner boundaries of an NGH-producing well and an artificial stimulation fracture for the first time. The device can realize the in situ hydrate formation prior to the experiment and axial loading application throughout the experiment. Both the strain control mode and the stress control mode can be achieved to estimate the deformation characteristics of HBS under different downhole conditions. Prime experiments proved their adaptability and reliability. The Ladetes provides an effective and alternative way of obtaining geotechnical parameters for HBS.

Displacement of piles from pressuremeter test results - a summary of French research and practice

This paper presents the ‘load-transfer functions’ t-z and p-y methods for determining the axial and lateral displacements of single piles. They are based on the results of pressuremeter tests. The methods from the results of the Ménard pre-borehole pressuremeter tests (MPM) and the self-boring pressuremeter tests (PAF, for Pressiomètre AutoForeur in French) are described. Especially, the t-z and p-y methods derived from the MPM test results are commonly used in the French practice. For both t-z and p-y curves, some theoretical background (usually FEM calculations in linear elasticity) is given. The results of the t-z and p-y analyses are compared to the measurements from loading tests on full scale piles. A proposal concerning barrettes is also presented.

Numerical simulations of experimental material testing in stone masonry arch railway bridges

This paper reports on a numerical study focused on the characterization of the masonry and infill material behaviour of stone arch railway bridges. The study is based on experimental data from testing campaigns carried out in materials of two granite stone bridges. The campaigns comprise lab tests on stone masonry samples (blocks and joints) collected from the bridge structure, as well as in-situ flat-jack testing and Ménard pressuremeter tests on masonry and infill components, respectively. A strategy was developed resorting to Finite Element (FE) methodologies involving local scale numerical simulation of the joint lab tests (shear tests) and both in-situ tests (Flat-jack and Ménard pressuremeter tests), aiming at the calibration and validation of the material parameters to be used in global scale numerical simulations of the bridges’ structural behaviour. The joint shear behaviour is simulated using a FE discrete formulation based on contact elements whereas the Flat-jack and Ménard pressuremeter testing is simulated using FE continuous homogeneous nonlinear materials based on a Drucker-Prager (D-P) model. The calibration of the D-P model input parameters is performed through a sensitivity analysis followed by an optimization strategy based on a genetic algorithm. The methodology showed the potential to calibrate the material constitutive parameters to be adopted in FE numerical models of this type of bridge.

Identifying parameters of a discrete numerical model of soil from a geotechnical field test

A discrete numerical model of a pressuremeter test was developed in this paper. The model is constituted of spherical particles with a contact law involving an inter-particle rolling resistance in addition to the classical Coulomb friction model. The model is calibrated from a pressuremeter test performed in the Hostun sand. An adaptive size of discretization of the soil domain is considered to limit the computational cost. Different parameter sets are defined to identify the initial density of the numerical granular assembly. Then, each parameter set leads to a different calibration of the mechanical parameters of the model in order to reproduce the pressuremeter test results. Simulations show that experimental data from a pressuremeter test alone are not enough to fully calibrate the discrete model. Other laboratory test results need to be considered in the calibration methodology. Eventually, the prediction capability of the model is assessed by comparing the simulated constitutive responses to those measured experimentally on different triaxial loading paths.

Comparing Engineering Properties from Small Diameter Pressuremeter Tests to Nuclear Density Unit Weights and Lightweight Deflectometer Stiffnesses in Cemented Coquina Base and Sandy Subgrades

Abstract Small diameter pressuremeter (SDPMT) equipment was developed and evaluated at four sandy embankment/roadbed sites in east-central Florida. These materials ranged from very loose to very dense. SDPMT tests were developed with the goal of supplementing or even replacing the nuclear density gauge (NDG) tests. SDPMT probes were placed in the pin holes made from NDG testing. Two probe lengths of 15 and 30 cm (6 and 12 in) were used, and two SDPMT testing procedures were used. One was the conventional incremental volume injection method and the second was a continuous injection process. Incremental tests were completed in about 15 min, whereas the continuous tests were completed in less than 1 min. SDPMT elastic moduli and limit pressures were obtained from 156 SDPMT tests. They were compared to dry unit weights from 96 NDG tests and 96 moduli from each of two lightweight deflectometer (LWD) models, one with digital load-deflection output and the other with input load and digital deflection output. One-hundred and twenty statistical models were developed describing the relationships between SDPMT, LWD, and NDG data. Linear, logarithmic, and exponential models were used. Ninety-three of the 120 models produced regression coefficients (R2) greater than 0.7, and 46 of the 120 produced R2 values greater than 0.8. Of the 40 models comparing SDPMT strength and stiffness to NDG dry unit weights, 12 or 30 %, produced R2 values greater than 0.8. Of the 40 models comparing SDPMT strength and stiffness to the Zorn LWD, 23 or 57.5 % produced R2 values greater than 0.8. Of the 40 models comparing SDPMT strength and stiffness to the Dynatest LWD, 11 or 27.5 % produced R2 values greater than 0.8. These models indicate that SDPMT strengths and stiffnesses are strongly correlated to NDG unit weights and LWD stiffnesses.

Stiffness decay characteristics and disturbance effect evaluation of structured clay based on in-situ tests

The structure of the sedimentary clay influences its mechanical behavior in non-negligible ways. This paper proposes an effective approach for investigating the in-situ stiffness characteristics from shear modulus and strain decay curves (G–γ curves) based on self-boring pressuremeter and seismic dilatometer tests. To evaluate the excavation disturbance effects on the structured clay, the stiffness parameters from pre-bored pressuremeter tests are compared with the results of self-boring pressuremeter tests. The result indicates that the complete in-situ G–γ curves can be acquired by integrating the strain-dependent tangent shear modulus Gt from self-boring pressuremeter tests and the small-strain modulus G0 from seismic dilatometer tests. Simultaneous observations of the G–γ curves with hyperbolic shapes in semi-logarithmic coordinates at the same strain scale show the similarity of the stiffness decay mode of the soil at different depths. The increase in the measured values of Gt and G0 with depth can be attributed to the improved consolidation pressures and cemented strength in the structured clay. Additionally, the G/G0–γ curves measured by the in-situ tests generally agree well with the results predicted by the Stokoe model. The excavation disturbance weakens the stiffness of the structured clay, as evidenced by Gt from the pre-bored pressuremeter data being significantly smaller than that from self-boring pressuremeter tests at the same depth. Based on quantitative analysis, the disturbance degree computed from the measured results has a low sensitivity to the soil depth and a strong negative correlation with the strain level of the soil. This study provides an effective method for predicting the stiffness parameters of structured soil based on in-situ tests.

Lateral response evaluation of single piles based on pressuremeter test results (using Foxta) versus standard penetration test results (using Lpile)

Lateral response evaluation of single piles based on pressuremeter test results (using Foxta) versus standard penetration test results (using Lpile)